H. B. Willman and Elwood Atherton
The Plaines Member of the Kankakee Formation (Willman, 1973, p. 18), the uppermost member, is named for Plaines Station, a railroad switching point on the southeast side of the Des Plaines River 1.75 miles southwest of Joliet, Will County.
The type section of the Plaines Member is at the top of a small quarry, where it overlies the type section of the upper part of the Troutman Member.
Extent and Thickness
The Plaines Member is 2.2 feet thick in the type section but elsewhere is 1.5-3.4 feet thick. It is widely exposed along the Kankakee and Des Plaines Rivers.
The dolomite of the Plaines Member is pure, massive, medium grained, and nearly white, and the top is the smooth surface that marks the top of the formation.
The Microcardinalia Zone is largely in the Plaines Member.
WILLMAN, H. B., 1973, Rock stratigraphy of the Silurian System in northeastern and northwestern Illinois: Illinois State Geological Survey Circular 479, 55 p.
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